Spirally wound paperboard tubes and paperboard composite tubes (tubes having one or more layers of paper and/or non-paper sheet material such as plastic, foil or the like), are used in a wide variety of applications throughout numerous industries. For example, spirally wound tubes are used as winding cores for winding filamentary materials such as yarns, threads and the like, and for winding of various sheet materials including paper, synthetic films, cloth, and other materials. Spirally wound tubes are also used as containers for food products such as frozen juices, bread doughs, and snack products; and as forms in the building industry, e.g., for forming concrete columns and the like.
Spirally wound tubes are traditionally formed by winding continuous plies of paperboard or other sheet material around a stationary mandrel. A plurality of strips or plies are fed onto the exterior of the mandrel in a radially layered relationship. Each of the plies is wound spirally onto the mandrel or onto an underlying ply so that the leading edge of each ply is positioned in contact with or adjacent the trailing edge of a preceding portion of the ply and so that each ply forms a radial layer of the tube. The individual plies are coated on one or both faces with a glue so that each layer is adhered to each radially adjacent layer to form a cylindrical tube wall. A rotating belt contacts the exterior of the layered tube as it is being formed on the mandrel and rotates the tube so that it moves spirally down the mandrel as it is being formed.
For various reasons, it is highly desirable to precisely control the relationship between the leading and trailing edges of the plies which define the spiral seam in the layers of the tube. If the leading and trailing edges of the ply are spaced from each other, a ply gap is formed which can adversely affect the strength and/or appearance of the tube. Similarly, uncontrolled overlapping of these edges can be highly undesirable. When the tubes are used as winding cores for film, paper or other thin sheet material, a gapped spiral seam or overlapped spiral seam on the exterior of the tube can adversely affect the appearance or quality of the sheet material wound onto the tube. In instances when the sheet material is wound tightly onto the tube, a gapped or overlapped spiral seam in an interior layer of the tube can also adversely affect the sheet material because of soft or hard spots caused by the seams. For similar reasons, spiral ply gaps are also undesirable in textile winding cores. In the food industry, spiral wound containers often contain exterior labels which are applied as the final spiral layer of the tube. In this case, it can be highly desirable to have a uniform registration between the leading and trailing edges of the ply because of printed instructions and/or patterns on the exterior, label layer of the tube.
Nonuniform spiral seams can be undesirable in the interior or intermediate layers of a spirally wound tube because of ply wrinkling that can result from the uneven seam and because uneven tension across a ply can harm adhesion of the ply to its adjacent outer or inner layer. Nonuniform spiral seams also can cause the tube to have a non-uniform strength along its length. In those instances when the inside layer of the tube includes a printed surface, or when the smoothness of the of the inside layer is important, e.g., when the tube is used to form a concrete column, nonuniform spiral seams are also highly undesirable.
For these and other reasons, careful attention is generally given to the spiral seam during the spirally wound tube manufacturing process. However, the seam uniformity is known to be difficult to control with precision because of numerous factors involved in the tube manufacturing process. These factors include variations in tension or construction of the winding belt, variations in the raw materials used in forming the tube or in the force of the motor driving the belt; adjustments by the operator in the speed of the manufacturing process, changes in the force required to pull the plies of paperboard or other material onto and along the mandrel due to irregularities in the ply or the feeding mechanism for the ply, changes in friction between the innermost layer of the tube and exterior of the forming mandrel; bending and other deformations of the winding mandrel or the drums supporting the winding belt; downstream forces which are applied to the tube such as the force from saws used to cut the tube into segments which can apply tensile or compressive forces along the length of the tube if the saw is not moved axially at precisely the same speed as the tube; and changes in the mass of the tube as tube sections are periodically cut from the end of the tube. The net result of any of these varying forces can be that the tube is moved down the mandrel at a varying rate with the result that nonuniform gaps can result between the adjacent edges of a ply in a single or multiple layers of the tube, and/or radial gaps can be formed between the radial layers of the tube.
The problem of nonuniform spiral seams has been addressed in various different ways as illustrated in the art. For example, U.S. Pat. No. 941,255 issued Nov. 23, 1909 to Jenkins employs a plurality of rollers mounted on the surface of the tube forming mandrel and a paper ply feeding mechanism which is mounted for axial movement with respect to the mandrel in order to overcome irregular movement of the winding belt. This is said to allow for variations in the position of the winding belt with respect to the tube forming mandrel by automatically adjusting the axial position of the ply feeding guide along the mandrel in response to such variations.
U.S. Pat. No. 3,150,575 issued Sep. 29, 1964 to Couzens et al. discloses a method for improving the uniformity of spirally wound paperboard tubes by employing two "eyes" or sensors which are spaced and monitor the spiral seam on the tube exterior at two spaced, spirally corresponding downstream locations. Any variations in the two corresponding seam locations, when detected, initiate adjustment of the helical lead or pitch of the wound tube by adjustment of the angle of inclination of the winding belts which wind the tube onto and along the mandrel.
U.S. Pat. No. 4,473,368, issued Sep. 25, 1984 to Meyer proposes a paper ply feeding mechanism which is supported on a frame that is rotatable with respect to the stationary mandrel. The spiral winding angle of the paper strips with respect to the axis of the mandrel is monitored during the tube manufacturing process and the so-called "pay out" or feed angle of the paper plies with respect to the mandrel is varied in response to any changes in the winding angle.
U.S. Pat. No. 5,425,693 to Gardner is directed to a method and apparatus for making spirally wound sleeves for printing cylinders wherein independently controllable motors are used to drive the drive belt that winds adhesive coated tapes onto a stationary forming mandrel in order to enhance control of the winding angle. The force and torque transmission of each motor is said to be independently controllable. In addition, the widths of the individual tapes can be slit on-line near the point of winding in order to precisely control the spiral gaps. The on-line slitting is controlled in response to a video camera which monitors the gap on the outer surface of the tube.
Despite these and other proposals to precisely control the spiral seam on paperboard and other spirally wound tubes, spiral seam uniformity remains a concern throughout the industry. This is particularly true when a high degree of precision is desirable. Although the above apparatus and methods and/or other known apparatus and methods can be used to control spiral seam uniformity with some degree of precision, the cost, complexity and reliability of the various methods and apparatus which are used for this purpose are such that there is no practical and reliable method and/or apparatus for ensuring spiral seam uniformity that is accepted throughout the industry, despite decades of experience in the manufacture of such tubes.